Field of the Invention
The invention relates to a method for fabricating a semiconductor component having a low contact resistance with respect to n.sup.+ -conducting or p.sup.+ -conducting, heavily doped zones in a semiconductor body, in which at least one titanium-containing layer is provided in a contact hole between the heavily doped zone and a contact metal connected to an external supply line.
Such a method is disclosed in U.S. Pat. No. 5,225,357. In that case, n.sup.+ -conducting or p.sup.+ -conducting, heavily doped zones are present which are connected, in a contact hole, to an external supply line through at least one titanium-containing layer and a contact metal applied thereto. Halogen is introduced into the heavily doped zones in the vicinity of the contact hole in order to reduce the contact resistance with respect to the heavily doped zone.
Furthermore, the implantation of fluorine ions in n-conducting silicon is described in a paper entitled: "Formation of Surface Inversion Layer in F.sup.+ -Implanted n-Type Silicon", by C. H. Chu et al., in Journal of Crystal Growth, Vol. 103, No. 1/4 (June 1990), Amsterdam, NL, pages 188 to 196.
In contact holes, a titanium layer and/or a titanium nitride layer serves as a barrier layer or layers in order to avoid diffusion from the semiconductor body into a contact layer, which is preferably composed of tungsten. Contacts of that type having a titanium/titanium nitride/tungsten layer sequence are provided, for example, on source and drain zones of CMOS transistors.
The contact resistance is undesirably large, particularly in contact holes having what is referred to as a high aspect ratio, that is to say a high value of the ratio between height and width of the contact hole. The same also applies to siliconized diffusion zones, that is to say zones formed by the reaction of silicon with titanium to form titanium silicide.
Increasing the layer thickness of the titanium layer would be conceivable for reducing the contact resistance. However, that is undesirable since the necessary layer thickness of the titanium layer should actually be reduced if only for reasons of saving material and microminiaturization.
Finally, thin oxide layers which are inevitably formed in the contact hole in the course of thermal processes also lead to disruptive effects and, in particular, to an increase in the contact resistance.
In addition to increasing the layer thickness of the titanium layer as mentioned above, consideration has also been given to collimated sputtering of titanium for forming the titanium layer, in order to ensure a reduction in the contact resistance. Another solution approach for decreasing the contact resistance is in the application of an additional sputtering and heat-treatment step for siliconizing the bottom of the contact hole. However, those two last-mentioned solution approaches for reducing the contact resistance, namely collimated sputtering of titanium and siliconization, are relatively complicated and have not yet achieved the desired results of a contact resistance which is sufficiently reduced in a simple manner.